Production of dimers of polyhydric alcohols



Pasta s, 193s 2,110,695

UNlTED STATES PATENT OFFICE George W. Batchelder, Woodbury, N. 1.. assigninto E. I. du Pont de Nemours & Company, Wilmington. DeL, a corporation of No Drawing. Application October 10, 1986, Serial No. 105,085

This invention relates to an improved method A further object is a method in which diglycerin of treating polyhydric alcohols for the production is obtained free from higher polymers and in of dimers of polyhydric alcohols and more parhigher yields than has been the case heretofore. ticularly to a process that brings about the pro- A still further object is a method in which blends duction of diglycerin from glycerin under condiof diglycerin with higher polymers of pre- 5 tions of high yield and purity. determined composition are obtained. Additional The polymers of glycerin have been produced, objects will be disclosed as the invention is furaccording to the prior art,'by heating glycerin at ther described hereinafter. elevated temperatures, 210-280 C. for example, I have found that the foregoing objects are for various intervals of time, under which condiaccomplished by first heating the glycerin to a 10 tions water is split out and condensation-polytemperature at which water is split of! and conmerization takes place. While simple heating of densation-polymeri'zation takes place, and then the glycerin is suflicient to bring about polymerisubjecting the reaction mixture to steam distillazation, the use of condensing agents has been protion under vacuum, which latter treatment not posed by a number of investigators. Some of the only distills the water and the glycerin from the 15 agents proposed for this purpose have comprised reaction mixture, but also depolymerizes the sulfuric acid, alkalis, sodium acetate, iodine, zinc higher glycerin polymers. chloride, and the like. The first step of my improved process, namely The use of condensing agents has in general the polymerization step, may be carried out in promoted the reaction and shortened the time rethe presence of condensing agents if desired. It 20 quired but has had the tendency to cause the. is more satisfactory, however, to carry out the formation of higher polymers than has been depolymerization in the absence of such agents, sired, except under very carefully controlled consince they promote the formation of the higher ditions. The object in polymerizing glycerin has polymers, and since they inhibit or retard the in general been the production of diglycerin, free subsequent depolymerization of these undesirable 25 from contamination with the higher polymers, polymers. The reaction mixture produced in the and this material has had its principal applicapolymerization step contains higher polymers of tion: in the explosives industry. Diglycerin on glycerin than the dimer. However, the subsenitration gives the compound known as tetrani quent treatment of the reaction mixture with su- 0 trodiglycerin, though more accurately designated perheated steam results in the depolymerization as diglycerin tetranitrate. When glycerin is of the higher polymers to diglycerin or glycerin. polymerized by heating, a satisfactory product The water. and the glycerin in the reaction mixcan be obtained having a diglycerin content of ture are distilled therefrom, by carrying out the between 30 and 45%, which on nitration gives a depolymerization step under a vacuum.

product substantially equivalent to nitroglycerin The following example will serve to illustrate 35 in explosive properties but offering much greater my process more exactly. It should be under- -resistance to freezing. stood, however, that this is illustrative only and It has been found very difilcult to obtain, by n no y limits y method of Procedure t the the methods of the prior art, a satisfactory qualdetails hereinafter set forth.

ity of diglycerin in concentrations higher than One thousand pounds of glycerin are polymer- 40 Excessive formation of higher polymers, ized by heating in a still under a vacuum of apsuch as triglycerin, tetraglycerin, and the like, proximately 6 inches of mercury, at about the occurson further heating and these higher polyboiling point of the material at the existing mers are unsuitable for nitration purposes. Dipressure. The heating is continued for 7 hours,

45 glycerin of relatively high purity can be obtained a-reflux condenser preventing any loss of glycerin 45 by careful fractionation of the glycerin-diglycbut permitting the evolved water to escape. At erin-polyglycerin solutions, but the yields obthe end of the heating or polymerization period, tained are insufilcient to make such a method the reaction mixture contains about 70% polycommercially desirable. When substantially mer, calculated as the dimer, although, of course,

pure diglycerin is wanted for industrial operaconsiderable amounts of the higher polymers are 50 tions, therefore, the prior art methods of producpresent. The reaction mixture is then steam distion are unsatisfactory. tilled for 1 /2 hours with steam preferably at a The object of my invention is an improved temperature of about 200 0., under a vacuum of method for the production of the substantially 28 to 29 inches of mercury. water and glycerin pure dimer of an aliphatic polyhydric alcohol. being collected in the distillate. The steam dis- 66 tillaflon' is discontinued when the economical stopping point has been reached, as determined a method not availableheretofore i'or obtaining'- substantially pure dlglycerin in yields-thatmake commercial operations. practicable." Whereas previous methods have been satisfactory where solutions of' 30 to 40% diglycerirr in glycerin were desired, the present method makes, it possible to obtain diglycerin-glycerin mixtures of more than diglycerin content,; andfree from higher condensation products. In such form the diglycerin is available for use in industrial processes or for .the preparation of its derivatives that may have application in organicindustries.

In' addition to the production of dlglycerin, it may be desired to produce a predetermined mixture of definite polymers of glycerin for utilization for certain purposes. Thiscanbe brought about by operating in general in accordance with the example given but controlling the amount of steam introduced to the predeterminedoptirnum quantity,'so that only the desired amount of the higher polymersare depolymerized.

In the foregoing description of my invention, I have applied it to the production of diglycerin from glycerin. It will be apparent, however, that it is equally applicable to the production of poly- -mers of many other aliphatic polyhydric alcotion, as here employed, refers to a reaction resulting in the formation of new bonds between atoms not already joined and proceeds with the elimination of elements or simple compounds. Polymerization is a chemical combination of a number of simple molecules to form a single molecule, a polymer being any compound formed by such a process and capable of being-degraded by the reverse process. Condensation-polymerization is a type of on in which the reaction proceeds with the elimination of simple elements or compounds.

It will be understood that man variations may be made from'the details of procedure described in the foregoing, without departure from the'spirit of the invention. I intend, therefore, to be limited only by the following patent claims.

I claim: 1. The process of producing the dimer of an aliphatic polyhydric alcohol which comprises -;l 1 eating said polyhydric alcohol to a temperature at which condensation-polymerization takes place and water issplit oil, and subsequently treating the reaction mixture, under reduced pressure, with steam.

2. The process of claim 1, in which the polyhydric alcohol is ethylene glycol.

3. The .process of claim 1, in whicli'the polysplitting oil of water, and subsequently treating the reaction mixture with ,a predetermined amount of superheated steam.

7. The process of producing substantially pure diglycerin which comprises heating glycerin to a temperature at which condensation-polymeri zation takes place, distilling the-water and glycerin under reduced pressure, and simultaneously introducing superheated steam into the reaction mixture. v

8. The process .of claim '7', in which the distil lation is carried out under a vacuum of at least 28 inches of mercury.

9. The process of dimerizing an aliphatic polyhydric alcohol which comprises heating said polyhydric alcohol to eflect polymerization thereof. and subsequently subjecting the reaction mixture to superheated steam distillation under vacuum to depolymerize the higher polymers and. to veilect the removal of the water and a substantial proportion of the monomer from said dimer.

10. The process of forming substantially pure diglycerin, which comprisu heating glycerin to effect the polymerization thereof, and subsequently subjecting the reaction mixture to superheated steam distillation under vacuum.

GEORGE W. 'BA'IUHELDER. 

